Patient-informed CRISPR Screen Identifies FLNB as a Novel Congenital Heart Disease and Ciliopathy Gene.

Heterotaxy (HTX) syndrome is a congenital disorder characterized by abnormal left-right organ placement, often leading to severe congenital heart defects (CHD). Despite advances in sequencing, many CHD/HTX-associated genes remain functionally unvalidated, hindering effective clinical diagnosis and management. Here, we leveraged a high-throughput CRISPR/Cas9 screening approach in the Xenopus model to rapidly evaluate candidate genes identified from whole-exome sequencing of human CHD patients. Our screen identified Filamin B (FLNB), an actin-binding protein previously linked to skeletal disorders but not to ciliopathies or CHD. We identified 5 probands with CHD/HTX, 3 with recessive, and 2 with damaging heterozygous mutations in FLNB. Disrupting FLNB in Xenopus reproduced key features of the human HTX phenotype, including defects in cardiac development and impaired motile cilia function. Rescue experiments confirmed the functional conservation of human FLNB, directly implicating actin cytoskeletal disruption in ciliogenesis and left-right patterning defects. Our results provide crucial evidence linking human FLNB dysfunction to ciliopathies and CHD/HTX.